1. Field of the Invention
This invention generally relates to a method for operating a multipoint control system. The invention more particularly relates to a method for operating a multipoint control system with serial data stream, especially is used for controlling lighting system such as LED lighting system.
2. Description of the Related Art
At present, there are three kinds of method to drive lighting device. One is that utilizing a control box for all of the lighting devices which coupled by several electric cables. This architecture is simple but one problem is a mount of cables is needed when a lots of lighting devices or distance between lighting device and the control box is too far, which costs too much. The second is common addressing bus architecture. The system is divided into several buses, each buses couple several lighting devices, each lighting device includes a control circuit and an unique ID, the system could work once power source and signal are provided. Common addressing bus architecture, however, includes several shortages such as a mount of lighting devices need setting different IDs, additional switches for controlling, EPROM cost, additional setting procedure, replacement of IDs when maintenance, etc. The third is serially connected controlling architecture. A lighting system includes a main control device to control several lighting devices, which could be divided into several sub-system coupled serially when the controlled point are far away from the main control device. Each sub-system serially connects each other, the main control device uses characteristic of shift registers to control data when and which device is transmitted to. Besides, a register signal is used to inform each controlled lighting device to capture data. In this way, it can simplify all of system in cable connection, setting and maintenance.
Referring to FIG. 1, it is a schematic diagram of a conventional control circuit of a serial connected lighting device. In fact, it is the third architecture described as above. In FIG. 1, it only shows five lighting device 101a-101e, cable signals 102 and 103 are the least need comprises data line DAT, clock line CLK, latch signal LE, output enable OE for brightness control, power source VDD and ground GND. Each of lighting devices 101a-101e coupled together by the connection signal 103.
Referring to FIG. 2, it is a block diagram of a lighting device shown in FIG. 1. There are only, but not limited to, four circuitry for explanation. Signal group 210 is input signal and signal group 211 is output signal. Four D type latches 203a˜203d construct a S-R shift register which receives a clock CLKI, stores DATI sequentially into the latches 203a˜203d and outputs inner data to the next lighting device through another data line DATAO.
After data shifting, the latch signal LEI drives four D type latches 203a˜203d to output data to another group D type latches 202a˜202d, then the LED driving circuit 201 drives the outside LED 213a˜213c, the buffer 206 is an output buffer for buffering data signals. Besides, output buffer may be built in some system for transmitting OEI, LEI and CLKI which extend distance between each of serially connected devices by amplifying data signal and clock signal. But the data latch signal is needed because of the data shifting. Therefore, three signal lines are needed between one point and another. It costs more and the reliability is lower when there are lots of point and far distance between these points. To improve this architecture, one method called clock fail detect is used to drive lighting device serially connected system. This kind of system needs to stop clock signal unnaturally and also limits the application of frequency of clock signal. In addition, it needs to retransmit all of data even though only one point needs update.
The second architecture is a system called DMX-512 or 12C. Each one of points needs a preset address, for example, which set by external DIP switches or by a programmable non-volatile memory. But setting is inconvenient and also causes high cost when maintain a part of system. An external addressing method and address coordination mechanism is provided, but still increases cost and complexity of design.
It is understood that a method for operating a multipoint system is needed in this market. The method is expected low cost, needs less control signals and selectively random addressing.